Systems and Methods for Reference Volume for Flow Calibration

ABSTRACT

A reference volume for use with pressure change flow rate measurement apparatus has an internal structure comprising elements with cross section and length comparable to the cross section and length of adjacent interstitial fluid regions. The reference volume may have one or more heat conduction elements exterior to and in good thermal contact with a corrosion resistant material that defines the internal fluid holding region.

PRIORITY CLAIM AND RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/334,323 filed Mar. 13, 2019, which is the National. Stage applicationof international application No. PCT/US17/052355, which claims thebenefit of U.S. Provisional Patent Application No. 62/396,809, filedSep. 19, 2016, entitled as “System and Methods for Reference Volume forFlow Calibration”, U.S. Provisional Patent Application No. 62/396,808,filed on Sep. 19, 2016, entitled as System, Apparatus and Methods forVariable Restriction for Flow Measurements and U.S. Provisionalapplication No. 62/396,807, filed on Sep. 19, 2016, entitled asapparatus and Methods for Self-Correcting Pressure based mass flowcontroller, which are each incorporated herein by reference in theirentirety.

FIELD

The present disclosure generally relates to determining the flow rate ofa fluid by measuring a temperature and a pressure of the fluid. Fluid asused herein is intended to encompass materials which are in a gaseousphase because of specific combinations of pressure and temperature. Theinvention is more particularly related to a containment used with apressure-volume-temperature (PVT) method of determining flow rates.

BACKGROUND

Determining the flow rate of a gaseous fluid by considering a time rateof change among one or more variables may be used. Devices using acombination of pressure, temperature, and volume, are common and oftenreferred to as using a PVT method. Typically, the device design isintended to hold two of those characteristics constant while allowingthe third to vary. Some devices, such as a bell prover or a pistonprover, are designed to hold the gas pressure and temperature constantduring a measuring time interval while allowing a contained volume tochange. Other devices, such as rate-of-rise (ROR) and rate-of-fall (ROF)apparatus, are designed to hold the gas temperature and volume constantduring a measuring time interval while allowing the pressure to changewithin a contained volume. All such flow measuring devices inherentlyhave limitations in the success at holding intended characteristicsconstant and limitations at measuring all variables, including the timeinterval. Measurement uncertainties arising from these limitations formthe primary constraints on the eventual accuracy of the determined flowrate.

In rate-of-rise and rate-of-fall apparatus an increasing or decreasingquantity of gaseous fluid is contained within a volume that isnotionally constant during a measuring time interval. This constantvolume for containing the measured fluid has been variously called a“reference volume,” or a “standard volume,” or a “known volume.” Thisdisclosure usually calls the subject constant volume a “referencevolume” but other similar terminology may be used. The reference volumeis remarked to be notionally constant because subtleties concerning theopening and closing of valves and other aspects of apparatus design canaffect the observed size of a reference volume but those subtleties arenot the primary focus of this disclosure. In semiconductor capitalequipment (sometimes referred to as “tools”) a reference volume may becomprised of one or more individual tank assemblies, or distributed asplumbing among various portions of a tool, or a combination of plumbingand tanks.

Flow rate determination methods based upon pressure change (ROR or ROF)in a reference volume typically require the fluid temperature to remainconstant during the measurement time interval. Maintaining isothermalconditions avoids having to deal with a time varying equation of state,and conveniently reduces most of the equation's mathematical partialderivatives to zero, thereby making the task computationally easier.

Other patents have described about Thermal mass flow meters. U.S. Pat.No. 6,539,791 issued to Weber describes about a calorimetric flowmeasuring device is characterized by a single thermistor for measuringflow. U.S. Pat. No. 6,628,202 issued to McQueen describes a thermaldispersion switch/transmitter for determining flow rate and liquid levelin a non-contacting apparatus. U.S. Pat. No. 7,107,835 issued toKorniyenko describes about a thermal mass flow sensor is disclosed thatincludes a housing having a sensor region and a thin film temperature.U.S. Pat. No. 8,870,768 issued to Kasim describes about devices andmethods useful for non-invasively measuring and indicating a rate offluid flow.

Hence there is a need for fabrication of a reference volume containmentwith best feasible thermal connection between the surface area enhancingstructures and the reference volume chamber walls. Suitable surface areaenhancing structures may be formed integral with a body of startingmaterial, while creating an interior void which functions as a fluidholding region within a reference volume chamber.

SUMMARY

Various embodiments include a flow controller system that comprises oneor more sensors, a flow measurement sensor that comprises one or moresensors. A reference volume for use with pressure change flow ratemeasurement apparatus has an internal structure comprising elements withcross section and length comparable to the cross section and length ofadjacent interstitial fluid regions.

In an embodiment of the disclosure, a reference volume body isdescribed, for use with a pressure change flow rate measurementapparatus comprising one or more fluid holding regions having boundariesformed by interior body material elements with cross section and lengthsimilar to the cross section and length of immediately adjacent portionsof the one or more fluid holding regions.

In another embodiment, a reference volume further including one or moreheat conduction elements exterior to and in good thermal contact with atleast a portion of a corrosion resistant material that forms theboundaries of at least one fluid holding region internal to thereference volume body. Wherein at least one heat conduction element ismade from copper, or a copper alloy, or aluminum, or an aluminum alloyand the corrosion resistant material that forms the boundaries of afluid holding region is made from a stainless-steel alloy, or anickel-chromium alloy, or a cobalt-chromium alloy, or titanium, ortantalum. A good thermal contact for the reference volume is made byshrink fit of a heat conduction element around a corrosion resistantmaterial, or brazing a heat conduction element to a corrosion resistantmaterial.

In yet another embodiment, a reference volume for use with a pressurechange flow rate measurement apparatus is described, including two ormore bodies, at least one body including at least one fluid holdingregion having boundaries formed by corrosion resistant material elementswith cross section and length similar to the cross section and length ofimmediately adjacent portions of the at least one fluid holding region,wherein at least two of the bodies are welded to each other and one ormore heat conduction elements in good thermal contact with the exteriorof a least one body.

In still yet another embodiment, a reference volume for use with apressure change flow rate measurement apparatus including two or morebodies, at least one body comprising at least one fluid holding regionhaving boundaries formed by corrosion resistant material elements withcross section and length similar to the cross section and length ofimmediately adjacent portions of the at least one fluid holding region,wherein one or more heat conduction elements are in good thermal contactwith the exterior of a least two adjacent bodies and the two adjacentbodies are made from stainless steel and the one or more heat conductionelements are made from copper.

Alternative embodiments relate to other features and combinations offeatures as may be generally recited in the claims. Embodimentsdescribed below allow parallel or serial processing of each methodand/or component.

In other embodiments, a reference volume can be designed so that heatconduction path lengths in the fluid, and heat conduction path lengthsin the reference volume mechanical structure, have similar timeconstants. This can be done for a specific choice of gas and structuralmaterial, but in most instances, would be done to accommodate a group ofgases (e.g. semiconductor process materials) and a particular structuralmaterial (e.g. stainless steel). The thermally conductive exteriorsecond material is meant to enhance uniformity of temperature over thelonger dimension(s) of the reference volume.

In alternative embodiments, a reference volume gets designed so anyslice along a plane keeps the gas and metal heat paths optimized(primary claim) in two dimensions. The exterior jacket then makes thethird dimension (length) relatively inconsequential. Besides internalfins and reference volume could merely be a bunch of parallel holes in asolid block, for example. But if there are too many holes in a clusterthen you get the same kind of problems as fins that are too long. Sooptimized holes will have a diameter about the same as thickness of theremaining metal web between them and might be not more than five holesacross entire bundle. The optimization process uses thermal diffusivityas a design consideration. Clearly other things like ability to measuremechanically, easy of fabrication, etc., may also be part ofoptimization.

Additionally, the flow controller work well by getting heat fromconcentrated sources (e.g. valve solenoid) distributed to everywhere(via thermal clamp onto reference volume) so there are nearly notemperature gradients within the whole device.

It should be understood that the summary above is provided to introducein simplified form a selection of examples that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of any claimed subject matter that may later claim priority tothe present description. Furthermore, the scope of any such claimedsubject matter would not be limited to implementations that solve anydisadvantages noted above or contained herein.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, wherein like reference numerals refer to like elements, inwhich:

FIGS. 1A, 1B and 1C are schematic diagrams of a reference volume for usewith pressure change flow rate measurement apparatus, according to anexemplary embodiment.

FIGS. 2A, 2B, 2C, 2D and 2E are schematic diagrams of a reference volumefor use with pressure change flow rate measurement apparatus, accordingto an exemplary embodiment.

FIGS. 3A, 3B, 3C and 3D are schematic diagrams of a reference volume foruse with pressure change flow rate measurement apparatus, according toan exemplary embodiment.

FIGS. 4A and 4B are schematic diagrams of a flow reference volume foruse with pressure change flow rate measurement apparatus, according toan exemplary embodiment.

FIGS. 5A, 5B and 5C are schematic diagrams of a reference volume for usewith pressure change flow rate measurement apparatus, according to anexemplary embodiment.

FIG. 6 illustrates a sample reference volume configuration.

FIG. 7 illustrates a sample reference volume configuration.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate the exemplaryembodiments in detail, it should be understood that the application isnot limited to the details or methodology set forth in the descriptionor illustrated in the figures. It should also be understood that theterminology is for the purpose of description only and should not beregarded as limiting.

Various embodiments are not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phrasing and terminology used herein isfor the purpose of description and should not be regarded as limiting.The use of “including,” “comprising,” or “having,” “containing,”“involving,” and variations thereof herein, is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems. The use of directional adjectives “inner, “outer,” “upper,”“lower,” and like terms, are meant to assist with understanding relativerelationships among design elements and should not be construed asmeaning an absolute direction in space nor regarded as limiting.

Heat transfer through a non-crystalline homogeneous material may becharacterized as a diffusion process whereby a local temperaturedifference drives heat energy from a region of higher temperature in thematerial into an adjacent region of lower temperature. The transfer ofheat is impeded by a thermal resistance of the material which mayequivalently be considered as the inverse of a thermal conductance. Theamount of heat energy (typically measured as Joules, calories, BTU, orsimilar units) required to raise the temperature of a region of thematerial by a specific amount (typically measured in degrees Celsius,degrees Fahrenheit, or Kelvin) directly depends upon the mass ofmaterial in the region and the heat capacity of the material. Heatcapacity of the material specified in terms of energy required to raisethe temperature of a specific mass by a specific amount then requiresknowledge of the material density to obtain an equivalent heat capacityfor a specific volume of the material. For example, the heat capacity ofpure water, at a pressure of one atmosphere and a starting temperatureof 15 degrees Centigrade (15° C.), is one calorie per gram per degreeCentigrade (cal/g*° C.), and one gram of water at that temperatureoccupies a volume of 1.0008722 cubic centimeters (density“rho”=0.9991286 gram/milliliter).

Consideration of the just described relationships matches a person'sdaily experience that a small amount of heat will make the small mass ofair above a flame immediately hot while the substantial mass of a metalutensil must be held in the same flame for quite some time before theend away from the fire becomes hot. Daily experience also illustratesthe low thermal conductivity of a wooden utensil makes the handleessentially never become hot while stirring boiling water and a metalutensil of high thermal conductivity in the same boiling water willeventually become entirely hot. The time rate at which a concentrationof heat diffuses within a material body, thereby making temperaturethroughout the body more uniform, thus can be described as being relatedto the thermal diffusivity of the material:

α=κ/ρCv  Equation 1.

-   -   “alpha equals kappa divided by product of rho multiplied by Cv”        where “alpha”=thermal diffusivity    -   “kappa”=thermal conductivity    -   “rho”=density    -   “Cv”=heat capacity at constant volume

In particular, Bracewell shows (The Fourier Transform and ItsApplications, ©1965, McGraw-Hill, Inc.) a localized elevated temperaturein a material body, as created by injecting an impulse of heat into thematerial body, will reduce according to a time factor:

SQRT{1/(α4πt)}  Equation 2.

-   -   “square root of the inverse product of alpha multiplied by four        pi time”

For simple comparisons the square root of the inverse of alpha issufficient:

tau=SQRT{1/α}  Equation 3.

An examination of time constants for various materials calculatedaccording to Equation 3 provides insight into the design of thermalstabilization structures intended for use in a reference volume in apressure change flow rate determination apparatus. There are minorvariations among reported material properties, such as heat capacity, inscience and engineering literature but disagreements of a few percentare irrelevant when considering time factor values that differ byfactors of four or five to one.

TABLE 1 material alpha (1.atm) SQRT{1/alpha} C2F6 3.91E−06 505.5 SF63.97E−06 501.7 Cl2 9.79E−06 319.6 CHF3 7.89E−06 356.1 CF4 8.59E−06 341.3HBr 1.14E−05 296.2 Ar 3.50E−05 169.1 N2 3.06E−05 180.6 O2 3.07E−05 180.6He 2.92E−04 58.5 CH4 4.97E−05 141.8 H2 2.11E−04 68.8 CO 2.95E−05 184.1CO2 1.39E−05 268.0 Ag 1.66E−04 77.7 Au 1.27E−04 88.7 Cu 1.11E−04 94.96061-Al 6.40E−05 125.0 304SS 4.20E−06 488.0 310SS 3.35E−06 546.2 Inconel600 3.43E−06 540.1 Mo 5.43E−05 135.7 Fe 2.30E−05 208.5 Si 8.80E−05 106.6quartz SiO2 1.40E−06 845.2 liquid H2O 1.43E−07 2644.4 Sn 4.00E−05 158.1

As shown in Table 1, thermal diffusivity (alpha=m{circumflex over( )}2/sec) of some typical gases varies by about seventy-five to one andthe corresponding time characteristic (tau=SQRT{1/alpha}) varies byabout one to nine. Also shown in Table 1, thermal diffusivity (alpha) ofsome solids varies by about one-hundred-twenty to one and thecorresponding time characteristic (tau) varies by about one to eleven.It is instructive to note thermal diffusivity of many gases at normalatmospheric conditions is similar to that of solids which might beconsidered materials of construction for a reference volume.

In particular, thermal diffusivity of stainless steels and corrosionresistant nickel alloys is nearly identical to thermal diffusivity ofgases comprised of larger and/or heavier molecules. This relationshipsuggests an optimal heat exchange structure within a stainless-steelreference volume should have fins, or other surface area enhancingstructures, with cross section and length similar to the portions of gasbetween those fins. Gases such as helium (He) and hydrogen (H2) can bevery effective heat transfer mediums but a pressure change flow ratedetermination apparatus for generalized use must also be suitable formeasuring common semiconductor industry gases such as chlorine (Cl2) andhexafluoroethane (C2F6).

If the thermal transfer aspect ratio of a fin is too high because ofinsufficient fin cross section and/or excessive fin length, then thetime needed to reach thermal equilibrium along a fin will be excessivewhen compared to thermal stabilization of the intermingled gas.Perforated sheet metal or screen type heat exchange structures with longaspect ratios are likely to be ill suited for moving heat into or out ofgas within a reference volume. The majority of a long aspect ratiostructure will be too far from the reference volume walls to have anyefficacy moving heat between the gas and the walls. If the fins are toothick then heat will not appropriately move from the middle of the finbulk toward or away from its surface in contact with the gas. Likewise,excessive thermal aspect ratio between a heat sink (temperaturestabilized) end of a reference volume and its central body may cause atemperature imbalance along the length of the reference volume.Excessive reference volume wall length will potentially causesignificant temperature gradients along the length of a referencevolume.

The thermal diffusivity of copper is about thirty times and aluminumabout twenty times that of stainless steel; therefore, copper oraluminum would be much better materials of construction for a referencevolume except for the potentially poor corrosion resistance. A superiorreference volume design may use one or more copper or aluminum heatconduction elements in good thermal contact with the exterior (away fromthe process gas) of a reference volume to enhance temperature uniformityalong the length of the reference volume. Heat conduction elements maybridge across weld joints, in a reference volume made from segments, soas to ensure good heat conduction across the joints.

Turning to the drawings and, in particular, FIG. 1A illustrates aperspective view of a containment 100A for a reference volume inaccordance with an exemplary embodiment. Iii general, the referencevolume containment 100A includes an inlet portion 110, a outlet portion120 and a reference volume chamber 130. A fluid and/or gas to bemonitored enters the reference volume chamber through the inlet portion110 and exits out from the outlet portion 120. The fluid and/or gas caninclude, but are not limited to common semiconductor industry gases suchas Chlorine (Cl2) and Hexafluoroethane (C2F6), water vapor, BoronTrichloride (BCl3), Silane (SiH4), Argon and Nitrogen. The interiorwalls of the reference volume chamber being capable of welding on to oneor more, thermal sensors, pressure sensors or PLCS (Programmable LogicControllers Systems).

The fluid inlet portion 110 may be capable of receiving fluid from oneor more sources. The reference volume chamber may be utilized as of oneor more isolated individual reference volume chamber, or distributed asplumbing part among various portions of a pipeline, or a combination ofplumbing and individual reference volume chambers. The inlet portion110, outlet portion 120 and reference volume chamber 130 may be madefrom corrosion resistant alloy. The corrosion resistant alloy caninclude, but not limited to Chrome, Stainless steel, Cobalt, Nickel,Iron, Titanium and Molybdenum. Different factors considered whilechoosing the alloy composition are ranges of alloy composition,parameters of heat treatment, complex material mixture metallurgy,degradation mechanisms and joining considerations. The reference volumechamber 130 may receive the fluid and/or gas from the fluid inletportion 110 and get in contact with other pressure/temperature sensorswithin the containment. The reference volume chamber 130 may perform thefunction of a thermal reservoir test cell during a rate of decaymeasurement of a fluid at constant temperature.

FIG. 1B describes a cross sectional view 100B along cutting plane B-B ofFIG. 1. The gaseous fluid entering through the inlet portion 110, entersinto the fluid holding region 140 and gets in contact with interiorwalls of the reference volume chamber 130 with a chamber base 150 and achamber ceiling 159. The reference volume chamber 130 and thus the fluidholding region 140 is partly bifurcated by a central wall 155 extendingfrom the chamber base 150 and not conjoined to the chamber ceiling 159,thereby creating a gap or pathway 157 for facilitating fluid movementfrom the inlet portion 110 to the outlet portion 120. The central wall155 may be made from corrosion resistant alloy similar to theconstruction of the reference volume chamber 130. The corrosionresistant alloy can include, but not limited to Chrome, Stainless steel,Cobalt, Nickel, iron, Titanium and Molybdenum.

The interior walls of the reference volume chamber or the central wall155 may be secured with one or more pressure sensors, temperaturesensors or welded on to one or more PCIS 170. The pressure sensor usedmay include, absolute pressure sensor, gauge pressure sensor, vacuumpressure sensor, differential pressure sensor and sealed pressuresensor. The temperature sensor used may include, a thermistor basedsensor for accurate temperature measurements. The PLCS 170 welded on tothe interior walls of the reference volume chamber and assist inmonitoring the pressure change flow rate measurements for the gaseousfluid entering inside the reference volume chamber 130 through the inletportion 110 and exiting out through the outlet portion 120. Theprogramming languages used for the PLCS 170 may be, but not limited to,function block diagram (FBD), ladder diagram (LD), structured text (ST;similar to the Pascal programming language), instruction list (IL;similar to assembly language), and sequential function chart (SFC).These techniques emphasize logical organization of operations.

The exterior walls of the reference volume chamber are circumferentiallyenveloped by a heat conduction element cover 160. The gaseous fluidentering the gaseous fluid holding region 140, gets in contact with thereference volume chamber walls, thereby getting in contact with thepressure sensors, temperature sensor or the PLCS and makes it way out ofthe reference volume chamber through the outlet portion 120. The heatconduction element cover helps in maintaining a constant temperature forthe fluid throughout the reference volume containment. A superiorreference volume design may use one or more copper or aluminum heatconduction elements cover 160 in good thermal contact with the exterior(away from the process gas) of a reference volume to enhance temperatureuniformity along the length of the reference volume. The heat conductionelement may be attached to the exterior walls of the reference volumechamber by autogenous orbital welding of circular connections orelectron beam welding of rectilinear and circular shapes or any suitableprocesses for sequential assembly of reference volume segments. The heatconduction element covers 160 helps in reducing excessive thermal aspectratio between a heat sink (temperature stabilized) end of a referencevolume chamber 130 and its central body leading to a temperatureimbalance along the length of the reference volume. Especially in caseof lengthy reference volume chamber 130 wall length, the heat conductionelement covers 160, will potentially reduce significant temperaturegradients along the length of a reference volume.

Many design choices and fabrication methods may be used to attachexterior heat conduction elements. In like manner, a reference volumechamber 130 may comprise a copper or aluminum body with a corrosionresistant material plated onto the surface of its interior fluid holdingregion 140. A reference volume chamber 130 may also comprise an interiorfluid holding region defined by a corrosion resistant sheet metal shellwith heat conducting material cast around its exterior. Other means ofattaching one or more heat conduction elements 160 against the exteriorof a reference volume chamber 130 include mechanical clamping, bondingwith thermally conductive adhesive (such as loaded epoxy cement),brazing, or shrink fit of a tubular copper or aluminum portion on theoutside of a cylindrical stainless steel portion that is inside.Shrink-fitting technique in which an interference fit is achieved by arelative size change after assembly is used to attach the heatconduction element 160 to the exterior walls of the reference volumechamber. This is usually achieved by heating or cooling one componentbefore assembly and allowing it to return to the ambient temperatureafter assembly, employing the phenomenon of thermal expansion to make ajoint. As the adjoined pieces reach the same temperature, the jointbecomes strained and stronger.

FIG. 1C describes a cross sectional view 100C along cutting plane C-C ofFIG. 1. The heat conduction element covers 140 circumferentiallyenveloping exterior walls of the reference volume chamber can bevisualized. The interior walls of the reference volume chamber 130 havea sine waved or an alternate trough and valley structured wall to givean enhanced surface area for contact for the gaseous fluid in thegaseous fluid holding region 140 with the interior walls of thereference volume chamber. It may be appreciated by anyone in the artthat other surface structures for enhancing the surface area for bettercontact of the gaseous fluid can also be implemented in the scope of theinvention.

In particular, thermal diffusivity of the base material for referencevolume chamber 130, is nearly identical to thermal diffusivity of gasescomprised of larger and/or heavier molecules. This relationship suggestsan optimal heat exchange structure within a stainless-steel referencevolume chamber should have fins, or other surface area enhancingstructures, with cross section and length similar to the portions of gasbetween those fins. Optimum heat transfer requires fins or surfaces thatextend from an object to increase the rate of heat transfer to or fromthe environment by increasing convection. The amount of conduction,convection, or radiation of an object determines the amount of heat ittransfers. Increasing the temperature gradient between the object andthe environment, increasing the convection heat transfer coefficient, orincreasing the surface area of the object increases the heat transfer.Thus, adding a fin to an object, increases the surface area and reducesheat transfer problems.

If the thermal transfer aspect ratio of a fin is too high because ofinsufficient fin cross section and/or excessive fin length, then thetime needed to reach thermal equilibrium along a fin will be excessivewhen compared to thermal stabilization of the intermingled gas. It isdesirable to have the best feasible thermal connection between thesurface area enhancing structures and the reference volume walls.Suitable surface area enhancing structures may be formed integral with abody of the reference volume chamber made of corrosion resistant alloyor stainless steel, while creating an interior void which functions as afluid holding region 140 within a reference volume chamber 130. Fins maybe formed by electric discharge machining (EDM—either wire or shapedelectrode), milling, drilling, turning, or like material removalprocesses. Extruded stainless-steel shapes are may be used. A referencevolume longer, or otherwise larger, than easily machined may befabricated as sections which are welded together in sequence, byautogenous orbital welding of circular connections or electron beamwelding of rectilinear and circular shapes are exemplary processessuitable for sequential assembly of reference volume segments.

In an alternative embodiment, the inner walls of the reference volumechamber can be maintained corrosion resistant by using wire meshstructures made of stainless steel. Generally, stainless steel a genericterm used to describe a steel alloy with a chromium content of 10.5% ormore. On the whole, stainless steels have a higher resistance tocorrosion than plain or carbon steel. This resistance to corrosion instainless steel is largely a result of the unique qualities of chromium.Chromium combines with oxygen in the atmosphere, naturally forming athin layer of chromium oxide. This extremely thin and invisible filmserves as a protective coating in a wide range of corrosiveenvironments. If the metal is cut or scratched and the film is ruptured,more oxide will quickly “self-repair” itself as to form and recover theexposed surface. The different wire mesh, which can be used forcorrosion resistance includes, but not limited to, T-304 stainlesssteel, T-316 stainless steel, T-310 SS, T-321 SS, T-347 SS, and evenT-430 SS. Another of the many benefits of T-304 SS is heat resistance.T-304 SS displays good oxidation resistance to a temperature ofapproximately 1600° F. in intermittent service and to a temperature of1700° F. in continuous service. T-304 stainless steel is also excellentfor fabrication purposes—it can be formed and cut to size withappropriate tools and machinery. It can also be welded, using mostcommon welding techniques, and it is virtually non-magnetic in theannealed condition. T-304 Stainless Steel is available in both woven andwelded constructions.

Referring to FIG. 2A, according to an exemplary embodiment, FIG. 2Aillustrates a perspective view of a containment 200A for a referencevolume. In general, the reference volume containment 200A includes aninlet portion 210, an outlet portion 220 and a reference volume chamber230. A fluid and/or gas to be monitored enters the reference volumechamber through the inlet portion 210 and exits out from the outletportion 220. The fluid and/or gas can include, but are not limited tocommon semiconductor industry gases or any other gas or gaseous mixturerequiring monitoring. The interior walls of the reference volume chamberbeing capable of welding on to one or more, thermal sensors, pressuresensors or PLCS (Programmable Logic Controllers Systems) or any othermonitoring sensor devices. The containment 200A is similar tocontainment 100A but differs in its internal structure for the fluidpathway.

The fluid inlet portion 210 may be capable of receiving fluid from oneor more sources or being connected to other reference volume chambersfor continuous monitoring. The inlet portion 210, outlet portion 220 andreference volume chamber 230 may be made from corrosion resistant alloy.The corrosion resistant alloy can include, but not limited to Chrome,Stainless steel, Cobalt, Nickel, Iron, Titanium and Molybdenum. Thereference volume chamber 230 may receive the fluid and/or gas from thefluid inlet portion 210 and get in contact with otherpressure/temperature sensors within the containment.

FIG. 2B shows a cross sectional view 200B along cutting plane B-B ofFIG. 2. The gaseous fluid entering through the inlet portion 210, entersinto the fluid holding region 240 and gets in contact with interiorwalls of the reference volume chamber 230 with a chamber base 250 and achamber ceiling 259. The reference volume chamber 230 and thus the fluidholding region 240 is partly interfered by a central tubular structure255 extending from the chamber base 250 and not conjoined to the chamberceiling 259, thereby creating a gap or pathway 257 for facilitatingfluid movement from the inlet portion 210 to the outlet portion 220. Thecentral tubular structure 255 may be made from corrosion resistant alloysimilar to the construction of the reference volume chamber 130. Thecorrosion resistant alloy may include, but not limited to Chrome,Stainless steel, Cobalt, Nickel, iron, Titanium and Molybdenum.

The interior walls of the reference volume chamber or the centraltubular structure 255 may be secured with one or more pressure sensors,temperature sensors or welded on to one or more PCLS 270. The exteriorwalls of the reference volume chamber are circumferentially enveloped bya heat conduction element cover 260. The gaseous fluid entering thegaseous fluid holding region 240, gets in contact with the referencevolume chamber walls, thereby getting in contact with the pressuresensors, temperature sensor or the PLCS and makes it way out of thereference volume chamber through the outlet portion 220 via the centraltubular structure 255 with a tubular pathway 258. The heat conductionelement cover helps in maintaining a constant temperature for the fluidthroughout the reference volume containment.

FIG. 2C describes a cross sectional view 200C along cutting plane C-C ofFIG. 2. The heat conduction element covers 260 circumferentiallyenveloping exterior walls of the reference volume chamber can bevisualized. The interior walls of the reference volume chamber 230 havea sine waved or an alternate trough and valley structured wall to givean enhanced surface area for contact for the gaseous fluid in thegaseous fluid holding region 240 with the interior walls of thereference volume chamber. It may be appreciated by anyone in the artthat other surface structures for enhancing the surface area for bettercontact of the gaseous fluid can also be implemented in the scope of theinvention.

The interior of the reference volume chamber 230 may be treated inalternative to avoid corrosion by employing corrosion inhibitors, whichare chemicals that react with the metal's surface or the environmentalgasses causing corrosion, thereby, interrupting the chemical reactionthat causes corrosion. The corrosion inhibitors can work by adsorbingthemselves on the metal's surface and forming a protective film. Thesechemicals can be applied as a solution or as a protective coating viadispersion techniques. The inhibitors process of slowing corrosiondepends upon, changing the anodic or cathodic polarization behavior,decreasing the diffusion of ions to the metal's surface and increasingthe electrical resistance of the metal's surface. The benefit ofcorrosion inhibitors is that they can be applied in-situ to metals as acorrective action to counter unexpected corrosion. Alternatively,organic coatings may be used to protect metals from the degradativeeffect of environmental gasses. Coatings are grouped by the type ofpolymer employed. Common organic coatings include, but not limited toalkyd and epoxy ester coatings that, when air dried, promote cross-linkoxidation, two-part urethane coatings, acrylic and epoxy polymerradiation curable coatings, vinyl, acrylic or styrene polymercombination latex coatings, water-soluble coatings, high-solid coatingsand powder coatings.

FIG. 2D illustrates another embodiment, where the reference volumechamber is full of vertical heat exchange tubes 270 that provide thermalmass and good surface area for heat exchange. In some embodiments, thetubes may not travel the entire length of the reference volume chamber,instead the tubes may be open at the top and bottom to allow the gas topermeate the entire volume of the reference volume. FIG. 2E illustratesa cross sectional area from FIG. 2D. The reference volume as circulartubes that pass through one or more quadrants of the reference volumechamber.

Referring to FIG. 3A, according to an exemplary embodiment, FIG. 3Aillustrates a partial perspective view of a containment 300A for areference volume. In general, the reference volume containment 300Aincludes a reference chamber 330 and heat conduction element cover 360.A fluid and/or gas to be monitored enters the reference volume chamberthrough an inlet portion (not shown) and exits out from the outletportion (not shown). The fluid inlet and outlet portions can be designedas in containment 100A or as in containment 200A. The fluid and/or gascan include, but are not limited to common semiconductor industry gasesor any other gas or gaseous mixture requiring monitoring. The interiorwalls of the reference volume chamber being capable of welding on to oneor more, thermal sensors, pressure sensors or PLCS (Programmable LogicControllers Systems) or any other monitoring sensor devices. Thecontainment 300A is similar to containment 100A/200A but differs in itsconstruction of the reference volume containment.

Referring to FIG. 3B, depicts an enlarged view 300B of containment 300Adescribed in FIG. 3A. The reference volume chamber 330 is enveloped by atwo-piece part of the heat conduction element cover 360. The two-pieceparts of the heat conduction element cover 360 are designed such thatthey can aptly fit on the outer walls of the reference volume chamber330.

Referring to FIG. 3C, describes a cross sectional view 300C alongcutting plane C-C of FIG. 3B. The reference volume chamber 330 isenveloped by a two-piece parts of heat conduction element cover 360forming part line 385. The two-piece parts of heat conduction elementcover 360 are fastened to each other by a pair of fasteners 390 on bothsides and secured with one or more pressure sensors, temperature sensorsor PLCS 370 for monitoring the gas flow through the reference volumechamber 330.

Referring to FIG. 3D, describes a cross sectional view 300D alongcutting plane D-D of FIG. 3B. The reference volume chamber 330 includesa fluid holding region 340 for the facilitating a free movement forfluids. The fluid inlet and outlet portions can be designed as incontainment 100A or as in containment 200A the reference volume chamberis enveloped by the heat conduction element 360.

Referring to FIG. 4A, according to an exemplary embodiment, FIG. 4Aillustrates a partial perspective view of a containment 400A for areference volume. In general, the reference volume containment 400Aincludes a reference chamber 430 and heat conduction element cover 460at the four corners of the reference volume chamber 430. A fluid and/orgas to be monitored enters the reference volume chamber through an inletportion (not shown) and exits out from the outlet portion (not shown).The fluid inlet and outlet portions can be designed as in containment100A or as in containment 200A. The fluid and/or gas can include, butare not limited to common semiconductor industry gases or any other gasor gaseous mixture requiring monitoring. The interior walls of thereference volume chamber being capable of fastened on to one or more,thermal sensors, pressure sensors or PLCS (Programmable LogicControllers Systems) or any other monitoring sensor devices. Thefasteners including, hardware devices that mechanically joins or affixestwo or more objects together. In reference to the present invention,fasteners are used to create non-permanent joints; that is, joints thatcan be removed or dismantled without damaging the joining components.The containment 400A is similar to containment 100A/200A/300A butdiffers in its construction of the reference volume containment.

Referring to FIG. 4B, describes a cross sectional view 400B alongcutting plane B-B of FIG. 4A. The reference volume chamber 430 isenveloped by a four-piece parts of heat conduction element cover 460 atthe four corners of the reference volume chamber 430. The heatconduction element covers 460 at the four corners of the referencevolume chamber 430 are secured with one or more pressure sensors,temperature sensors or PLCS for monitoring the gas flow through thereference volume chamber 430.

Referring to FIG. 5A, according to an exemplary embodiment, FIG. 5Aillustrates a partial perspective view of a pipeline containment 500Afor a reference volume. In general, the pipeline reference volumecontainment 500A includes a reference volume chamber 530 and heatconduction element cover 560 at the terminal ends of the pipelinereference volume chamber 530. Additionally, the pipeline referencevolume can be wrapped with filler heat conduction elements 590 to drivethe temperature to ambient temperatures that are outside the mass flowcontroller. A fluid and/or gas to be monitored enters the referencevolume chamber through one end of pipeline and exits out from anotherend of pipeline. The fluid and/or gas can include, but are not limitedto common semiconductor industry gases or any other gas or gaseousmixture requiring monitoring. The interior walls of the reference volumechamber being capable of welding on to one or more, thermal sensors,pressure sensors or PLCS (Programmable Logic Controllers Systems) or anyother monitoring sensor devices. The containment 500A is similar tocontainment 100A/200A/300A/400A but differs in its construction of thereference volume containment.

Referring to FIG. 5B, describes a cross sectional view 500B alongcutting plane B-B of FIG. 5A. The reference volume chamber 530 isenveloped by a two-piece parts of filler heat conduction element cover590 and all through the pipeline tubing by a heat conduction elementcover 560. The heat conduction element covers 560 secured with one ormore pressure sensors, temperature sensors or PLCS for monitoring thegas flow through the reference volume chamber 530.

Referring to FIG. 5C, describes a cross sectional view 500C alongcutting plane C-C of FIG. 5A. The pipeline reference volume chamber 530includes a fluid holding region 540 for facilitating a free movement forfluids. The fluid inlet and outlet portions can be designed as incontainment 100A or as in containment 200A the reference volume chamberis enveloped by the heat conduction element 560.

Referring to FIG. 6, FIG. 6 describes a system 600, which can basicallybe combined with a flow control apparatus system. The flow pathway forthe fluid entry into the system 600 begins with “A” and then along thedirection of “B” and then to “C”, where after the fluid is pushed along“Cl” raising to the terminal end of “Cl” and pours back downwardstowards “D” and then moves along “E” and then to “F” and finally exitsthrough “G”. A flow transducer sensing element 610 is mountedperpendicular to the gas flow for making any required measurements. Flowtransducers are used to measure fluid flow velocity. Flow transducersare based on analysis of the flow velocity, to calculate the flow levelor determine the amount of flow within a chamber. The flow pathwaydescribed above can be implemented in any of the reference volumecontainment described in 100A/200A/300A/400A/500A.

An apparatus for reference volume measurements, includes a referencevolume chamber, an interior region of the reference volume chambercomprising of an inlet portion, a bottom portion, a finned structuredside wall and a central wall, that defines a fluid boundary for a fluidpathway for a fluid, entering through the inlet portion, sensed via atransducer element mounted orthogonal to the fluid pathway and exitingthrough the outlet portion of the reference volume chamber.

An apparatus for measurement of pressure including one or more pressuresensing elements, in a fluid pathway for a fluid, entering through theinlet portion, the fluid sensed via a transducer element mountedorthogonal to the fluid pathway and exiting through the outlet portionof the overall fluid pathway. In other words, the diaphragm is parallelto the flow of the gas while the length dimension of the transducer isperpendicular to gas flow.

Referring to FIG. 7, FIG. 7 describes a system 700, which shows thefluid pathway in an exemplary heat exchanger 710. An initial gas flowaligned in the direction A-B is deliberately diverted along aperpendicular direction along C-D to provide more residence time andmore temperature stabilization by better heat exchange around a finnedstructure 720. The finned structure may be having a plain structure,which refer to simple straight-finned triangular or rectangular designs;herringbone structure, where the fins are placed sideways to provide azig-zag path; and serrated and perforated which refer to cuts andperforations in the fins to augment flow distribution and improve heattransfer.

Having thus described several aspects of at least one embodiment, is tobe appreciated various alterations, modifications, and improvements willreadily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be part of thisdisclosure, and are intended to be within the scope of the invention.Accordingly, the foregoing description and drawings are by way ofexample only.

The construction and arrangement of the systems and methods as shown inthe various exemplary embodiments are illustrative only. Although only afew embodiments have been described in detail in this disclosure, manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.). For example, the position of elements may bereversed or otherwise varied and the nature or number of discreteelements or positions may be altered or varied. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure. The order or sequence of any process or method stepsmay be varied or re-sequenced according to alternative embodiments.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions and arrangement of the exemplaryembodiments without departing from the scope of the present disclosure.

The present disclosure contemplates methods, systems and programproducts on any machine-readable media for accomplishing variousoperations. The embodiments of the present disclosure may be implementedusing existing computer processors, or by a special purpose computerprocessor for an appropriate system, incorporated for this or anotherpurpose, or by a hardwired system, or a printer circuit board.Embodiments within the scope of the present disclosure include programproducts comprising machine-readable media for carrying or havingmachine-executable instructions or data structures stored thereon. Suchmachine-readable media can be any available media that can be accessedby a general purpose or special purpose computer or other machine with aprocessor. By way of example, such machine-readable media can compriseRAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any other mediumwhich can be used to carry or store desired program code in the form ofmachine-executable instructions or data structures and which can beaccessed by a general purpose or special purpose computer or othermachine with a processor. When information is transferred or providedover a network or another communications connection (either hardwired,wireless, or a combination of hardwired or wireless) to a machine, themachine properly views the connection as a machine-readable medium.Thus, any such connection is properly termed a machine-readable medium.Combinations of the above are also included within the scope ofmachine-readable media. Machine-executable instructions include, forexample, instructions and data which cause a general-purpose computer,special purpose computer, or special purpose processing machines toperform a certain function or group of functions.

Although the figures may show a specific order of method steps, theorder of the steps may differ from what is depicted. Also, two or moresteps may be performed concurrently or with partial concurrence. Suchvariation will depend on the software and hardware systems chosen and ondesigner choice. All such variations are within the scope of thedisclosure. Likewise, software implementations could be accomplishedwith standard programming techniques with rule based logic and otherlogic to accomplish the various connection steps, processing steps,comparison steps and decision steps.

What is claimed is:
 1. A system for reference volume measurements,comprising: a reference volume chamber with an inlet portion and anoutlet portion for a fluid through the reference volume chamber; aninterior region of the reference volume chamber having a bottom wall, aceiling wall, a central wall and a side wall, wherein the side wall andthe central wall extends from the bottom wall and not conjoined with theceiling wall, thereby making a gap for fluid movement; an exterior wallof the reference volume chamber enveloped by a heat conduction cover forproviding a thermal conduction so that the temperature is affected byambient effects for the fluid in the reference volume chamber; and thecentral wall and the side wall capable of being secured with one or moresensors or programmable logic controllers (PLCs).
 2. The system forreference volume measurements, as described in claim 1, wherein the oneor more sensors is a thermal sensor chosen from a group of NegativeTemperature Coefficient (NTC) thermistor, Resistance TemperatureDetector (RTD), Thermocouple or Semiconductor-based sensors.
 3. Thesystem for reference volume measurements, as described in claim 1,wherein the one or more sensors is a pressure sensor chosen from a groupabsolute pressure sensor, gauge pressure sensor, vacuum pressure sensor,differential pressure sensor or sealed pressure sensor.
 4. The systemfor reference volume measurements, as described in claim 1, wherein thecentral wall has a tubular structure and connects directly to the outletportion of the reference chamber.
 5. The system for reference volumemeasurements, as described in claim 1, wherein the PLCs use programminglanguages from group comprising of function block diagram (FBD), ladderdiagram (LD), structured text (ST; similar to the Pascal programminglanguage), instruction list (IL; similar to assembly language) andsequential function chart (SFC).
 6. The system for reference volumemeasurements, as described in claim 1, wherein the side wall has afinned stricture, the central wall, the bottom wall and the ceiling wallare made of corrosion resistant alloy.
 7. The system for referencevolume measurements, as described in claim 1, wherein the interior sidewall, the central wall, the bottom wall and the ceiling wall are treatedwith a corrosion resistant coating.
 8. The system for reference volumemeasurements, as described in claim 1, wherein the side wall, thecentral wall, the bottom wall and the ceiling wall are covered with acorrosion resistant wire mesh.
 9. The system for reference volumemeasurement, as described in claim 1, wherein the fluid is chosen from agroup comprising of semiconductor industry gases such as Chlorine (Cl2)and Hexafluoroethane (C2F6), water vapor, Boron Trichloride (BCl3),Silane (SiH4), Argon and Nitrogen.
 10. The system for reference volumemeasurement as described in claim 1, wherein the side wall, the centralwall, the bottom wall and the ceiling wall are made of material chosenfrom a group comprising of Chrome, Stainless steel, Cobalt, Nickel,Iron, Titanium and Molybdenum.
 11. The system for reference volumemeasurement as described in claim 1, wherein the heat conduction elementis chosen from a group comprising of copper or aluminum.
 12. The systemfor reference volume measurement as described in claim 1, wherein theheat conduction cover is attached to the exterior wall of the referencevolume chamber by a method chosen from a group comprising of mechanicalclamping, bonding with thermally conductive adhesive, brazing, or shrinkfit methodologies.
 13. The system for reference volume measurement asdescribed in claim 1, wherein the reference chamber is fabricated assections which are welded together in sequence, by autogenous orbitalwelding of circular connections or electron beam welding of rectilinearand circular shapes.
 14. The system for reference volume measurement asdescribed in claim 1, wherein the interior side wall, the central wall,the bottom wall and the ceiling wall are covered by a wire mesh chosenfrom a group comprising of T-304 stainless steel, T-316 stainless steel,T-31.0 SS, T-321 SS, T-347 SS or even T-430 SS.
 15. The system forreference volume measurements as described in claim 1, wherein thesystem can be used an individual unit.
 16. The system for referencevolume measurements as described in claim 1, wherein the system can beemployed as a part of complex unit comprising of one or more referencevolume chambers.
 17. The system for reference volume measurements asdescribed in claim 1, wherein the system can be employed as a part of apipeline structure.
 18. The system for reference volume measurements asdescribed in claim 17, wherein the system has one or more filler heatconduction cover in addition to the heat conduction cover.
 19. Anapparatus for measurement of pressure, comprising: one or more pressuresensing elements, in a fluid pathway for a fluid, entering through theinlet portion, sensed via a transducer element mounted orthogonal to thefluid pathway and exiting through the outlet portion of the overallfluid pathway.
 20. A system for reference volume measurements,comprising: a reference volume chamber with an inlet portion and anoutlet portion for a fluid to pass through the reference volume chamber;the reference volume chamber having a heat exchanger chamber; wherein afluid entering a horizontal direction into the reference volume chamberis capable of being diverted to a vertical direction through the heatexchanger chamber to achieve a temperature stabilization during a rateof decay operation.